Compelled duel only has 1 target so it is suitable to be twinned. But some events such as if I attack either creature under the spell reads as if the spell ends on both targets. This seems true for ending my turn more than 30ft away from either one as well?
When the spell ends for one, the spell ends for both, and this makes compelled duel totally unusable.
The last sentence of compelled duel says (emphasis mine):
The spell ends if you attack any other creature, if you cast a spell that targets a hostile creature other than the target, if a creature friendly to you damages the target or casts a harmful spell on it, or if you end your turn more than 30 feet away from the target.
The spell ends when you trigger one of these end conditions for either target, and since the one spell has ended, it no longer affects the other target.
In contrast, this answer details a scenario where a dispel magic only ends the effect for one of the targets of a twinned spell. Notably, it works because of the language of dispel magic (emphasis mine):
Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends.
Dispel magic specifies the spell ends for that target only, not that the spell ends outright, as it would in our scenario with compelled duel.
But let's examine the details of each end condition. The spell ends...
If you attack another creature
Twinned Spell allows both creatures to be each independently subject to the effects of compelled duel. Therefore, the spell ends even if the other creature you attack is the other one you targeted with compelled duel. The other creature is "another creature".
Therefore, under no circumstances should you twin compelled duel, as attacking either creature would end the spell entirely. Simply attacking one of the creatures would trigger the end condition on the other and end the spell outright.
If you cast a spell that targets a hostile creature other than the target
Again, same problems as the previous section. If you target either creature with a spell, compelled duel immediately ends for both creatures.
If a creature friendly to you damages the target or casts a harmful spell on it
If any of your friends targets either of the compelled creatures, the spell ends immediately on both. This is bad, as it reduces the number of creatures you're allies are able to attack without ending your spell. But maybe it's not bad, since the spell is almost totally useless here.
If you end your turn more than 30 feet away from the target.
So now you have to manage your distance from two creatures, instead of one, in order to maintain your now useless spell.
Conclusion: Twinned Spell makes compelled duel totally unusable.
Twinned spell makes it so that doing basically anything to the targeted creatures end the spell. And it should. The entire point of compelled duel is to have a one-on-one duel with another creature, and so it seems natural (at least to me) that double dipping wouldn't work.